Not for the first time, human rights violations by a Middle Eastern tyrant pose a dilemma for leftists on both sides of the Atlantic. On the one hand, they don't like reading about people being gassed. On the other, they are deeply reluctant to will the means to end the killing, for fear of acknowledging that western – meaning, in practice, American – military power can be a force for good.

Ever since the 1990s, when the United States finally bestirred itself to end the post-Yugoslav violence in the Balkans, I have made three arguments that the left cannot abide. The first is that American military power is the best available means of preventing crimes against humanity. The second is that, unfortunately, the US is a reluctant "liberal empire" because of three deficits: of manpower, money and attention. And the third is that, when it retreats from global hegemony, we shall see more not less violence.

More recently, almost exactly year ago, I was lambasted for arguing that Barack Obama's principal weaknesses were a tendency to defer difficult decisions to Congress and a lack of coherent strategy in the Middle East. Events have confirmed the predictive power of all this analysis.

To the isolationists on both left and right, Obama's addiction to half- and quarter-measures is just fine – anything rather than risk "another Iraq". But such complacency (not to say callousness) understates the danger of the dynamics at work in the Middle East today. Just because the US is being led by the geopolitical equivalent of Hamlet doesn't mean stasis on the global stage. On the contrary, the less the US does, the more rapidly the region changes, as the various actors jostle for position in a post-American Middle East.

Syria today is in the process of being partitioned. Note that something similar has already happened in Iraq. What we are witnessing is not just the end of the Middle East of the 1970s. This could be the end of the Middle East of the 1920s. The borders of today, as is well known, can be traced back to the work of British and French diplomats during the first world war. The infamous Sykes-Picot agreement of 1916 was the first of a series of steps that led to the breakup of the Ottoman empire and the creation of the states we know today as Syria and Iraq, as well as Jordan, Lebanon and Israel.

As we approach the centenary of the outbreak of the first world war, there is no obvious reason why these states should all survive in their present form.

It is tempting to think of this as a re-Ottomanisation process, as the region reverts to its pre-1914 borders. But it may be more accurate to see this as a second Yugoslavia, with sectarian conflict leading to "ethnic cleansing" and a permanent redrawing of the maps. In the case of Bosnia and Kosovo, it took another Democrat US president an agonisingly long time to face up to the need for intervention. But he eventually did. I would not be surprised to see a repeat performance if that president's wife should end up succeeding Obama in the White House. After all, there is strong evidence to suggest Obama agreed to the original chemical weapons "red line" only under pressure from Hillary Clinton's state department.

Yet the president may not be able to sustain his brand of minimalist interventionism until 2016. While all eyes are focused on chemical weapons in Syria, the mullahs in Iran continue with their efforts to acquire nuclear weapons. The latest IAEA report on this subject makes for disturbing reading. I find it hard to believe that even the pusillanimous Obama would be able to ignore evidence that Tehran had crossed that red line, even if it was drawn by the Israeli prime minister rather than by him.

The Iranian factor is one of a number of key differences between the break up of Yugoslavia and the breakup of countries like Syria and Iraq.

The Middle East is not the Balkans. The population is larger, younger, poorer and less educated. The forces of radical Islam are far more powerful. It is impossible to identify a single "bad guy" in the way that Slobodan Milosevic became the west's bete noire. And there are multiple regional players – Iran, Turkey, the Saudis, as well as the Russians – with deep pockets and serious military capabilities. All in all, the end of pan-Arabism is a much scarier process than the end of pan-Slavism. And the longer the US dithers, the bigger the sectarian conflicts in the region are likely to become.

The proponents of non-intervention – or, indeed, of ineffectual intervention – need to face a simple reality. Inaction is a policy that also has consequences measurable in terms of human life. The assumption that there is nothing worse in the world than American empire is an article of leftwing faith. It is not supported by the historical record.